If you’ve ever seen car advertisements trumpeting a five-star safety rating or seen photos or videos of vehicles covered in high-visibility stickers being smashed into walls, you’ve been exposed to the work of the National Highway Traffic Safety Administration (NHTSA) or the Insurance Institute for Highway Safety (IIHS). These agencies perform vehicle safety tests that have likely made you and your passengers safer and may even have influenced your car buying decisions. Stars aside, how much do you really know about the meaning behind these popular safety ratings?

National Highway Traffic Safety Administration Ratings

The NHTSA’s vehicle ratings are the star rating system, with five stars at the top of the range. Whether in ads for a new BMW for sale or reviews for the best used cars, you’ve likely seen 5-Star Overall Safety Rating references touted as a selling point. These NHTSA ratings are based on how your car performs in three types of collisions: a head-on (frontal) collision and two forms of side impacts. Additionally, the NHTSA considers your vehicle’s resistance to rollover, based on a calculation including top-heaviness and maneuverability.

For each of the crash tests, dummies that approximate the size or weight of an “average” person are placed in various locations to record the potential for you or your passengers to be injured in various ways. If you are smaller than the average person, keep in mind that these tests might under-represent how badly injured you might be in similar scenarios.

The NHTSA evaluates your car’s likelihood of inflicting crash injuries a bit differently depending on which type of crash is being simulated. In the frontal crash scenario, examiners are especially interested in potential injuries to your head and neck, your torso, and your leg. Side crash tests add assessments of injuries to your abdomen, spine, and pelvis.

Insurance Institute of Highway Safety Ratings

Ratings from the IIHS involve a few more variables than the NHTSA’s straightforward crash tests. IIHS crash testing includes “moderate overlap” frontal crashes, driver and passenger side frontal crashes (small overlap), and side crashes. In addition to these crash performance tests, the IIHS vehicle reviews also consider any features that a vehicle has that could help avoid a crash or reduce its impact.

The IIHS assigns vehicles a rating of either Good, Acceptable, Marginal, or Poor. Some of the criteria factored into each model’s score include the following:

  • Performance of the car’s safety cage in protecting passengers from crash forces
  • Amount, type, and severity of “injuries” to test dummies
  • Occupant movement indicating the effectiveness of seatbelts and other restraints
  • Additional safety features like seatbelt reminders and child safety seat latches

Like the NHTSA, the IIHS typically tests only newly introduced vehicles or models that have had significant updates that could affect their crash test results.

Knowledge Is Safety

Given how good safety ratings are promoted by car manufacturers, you’d be wise to investigate a vehicle’s safety performance in depth before you buy. While the overall rating of a vehicle can give you some reassurance, diving a bit deeper into the underlying results shows you the full picture. The more you know about the good, bad, and mediocre parts of a car’s safety ratings, the more equipped you are to judge whether it’s a safe choice for your family.